A tad warmer perhaps with a tad more bass and a bit smoother in the mid range but certainly very close in sound signature to the 450 Pro. Soundstaging is about the same as well. 435S a tad more "booring" whereas the 450 Pro are a bit juicier at times. Perhaps a bit more "sparkle" in the highs

The 435S allow earpad rolling which the 450 Pro doesn´t. I haven´t yet had time to listen to them more then the stock earpads though. Stock earpads are the same as on the 450 Pro and 8.35D monitors. The replacement pads are also the same that is offered for the 8.35D Monitors

edit: I tried my favourite replacement earpads for the 8.35D Monitors. the pleather oval earpads. Made quite a dramatic change in the sound signature on those but here it´s much more modest. They get slightly less bass and a tad colder as a result. Also got a bit sibilant. My ears got sweaty like on the 8.35D Monitors with those pads as well. Still pleasent but for a lot of music just got a bit to lean. I have lower expectations on the velour pads but will have to try that some other day.

Read your review. Agree for me it´s either stock or the 6085 pads. Velour without vent holes. The rest I could dismiss quite easilly. The oval pleather pads made them just to cold and anemic. The velour pads with went holes just didn´t sound right either.

It´s smoothness/forgiveness/warmth vs detail pretty much stock vs 6085. You remove the filters when you use custom ear pads thus they get a bit more detailed. Need more time but they feel even better balanced on that. Feels like it put more strain on my ears though so will see what I go for in the long run.

As for soundstage hoped a bit more since it´s fully open but listening to nils Lofgren Accoustics Life it´s not quite as clear as the Pro 900. There you get the singer right in front of you like I get with my speakers where on the 435S I can hint I have him in both my left and right ear. Same with audience clapping and such the positioning is a bit more blurred but it´s not that far behind.